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Coordinated Regulation of Glycogen Synthesis and Breakdown:- Transport into Cells Can Limit Glucose Utilization

المؤلف:  David L. Nelson، Michael M. Cox

المصدر:  Lehninger Principles of Biochemistry

الجزء والصفحة:  588

2026-06-08

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Coordinated Regulation of Glycogen Synthesis and Breakdown:- Transport into Cells Can Limit Glucose Utilization

The passive uptake of glucose by muscle and adipose tissue is catalyzed by the GLUT4. In the absence of insulin, most GLUT4 molecules are sequestered in membrane vesicles within the cell, but when blood glucose rises, release of insulin triggers GLUT4 movement to the plasma membrane. Glucose transport into hepatocytes involves a different, high-capacity transporter, GLUT2, which is always present in the plasma membrane. It catalyzes facilitated diffusion of glucose in both directions, at a rate high enough to ensure virtually instantaneous equilibration of glucose concentration in the blood and in the hepatocyte cytosol. In its role as a glucose sensor, the glycogen phosphorylase of hepatocytes is essentially measuring the glucose level in blood.